Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.37	4.131%	$257.5889	$257.59	$257.60	$257.60
Purchase #2	$135.39	9.689%	$148.5079	$148.51	$148.50	$148.50
Purchase #3	$132.71	9.411%	$145.1993	$145.20	$145.20	$145.20
Purchase #4	$142.53	6.523%	$151.8272	$151.83	$151.85	$151.80
Purchase #5	$99.54	5.814%	$105.3273	$105.33	$105.35	$105.30
Purchase #6	$50.36	7.817%	$54.2966	$54.30	$54.30	$54.30
Purchase #7	$205.55	9.455%	$224.9848	$224.98	$225.00	$225.00
7 purchase totals =	$1,013.45		$1,087.7320	$1,087.74	$1,087.80	$1,087.70